If your phone's battery indicator perpetually shows one bar, a portable battery charger can get you through the day, but that charger also needs to be charged. Enter the MyCharge TransitPlus, which comes with its own swing-out plugs for wall and car charging.

At 3.7 inches by 2.4 inches, the TransitPlus has the length and width of a deck of cards, but is a bit thicker at 1.1 inches. Only weighing a third of a pound, it slips into coat pockets and bags easily, or can be stored in a glove box or cupholder in a car.

Glossy carbon-fiber-patterned sides give the device an attractive, modern look. MyCharge keeps the design smooth with one recessed button, four white LEDs, and, most important, a standard wall plug and 12-volt car plug that recess into the body of the TransitPlus. The main pin for the 12-volt and the prongs for the wall outlet stick out just a little, but are not likely to snag other items in a purse or pocket.

Unlike the MyCharge Peak 6000 Powerbank , which includes USB, Mini-USB, and 30-pin iOS device plugs, the TransitPlus keeps it simple with a single USB port. You will need to bring your own adapter cords for whichever devices you want to charge on the go.

At 3,000 milliamp-hours (mAh), the battery capacity of the TransitPlus is only half that of the Peak 6000 Powerbank. However, 3,000mAh is enough to fully charge a dead iPhone 5S , with its 1,900mAh battery, or a Samsung Galaxy S5 , which has a 2,800mAh battery. It will bring an iPad up to a 25 percent charge, and restore 75 percent of the battery capacity on a Nexus 7 .

The 1 amp output from the TransitPlus' USB port is equivalent to a standard phone charger. Tablet charging times will be considerably slower, as those devices typically require a higher output. However, TransitPlus has a trick up its conduit -- you can plug it into a wall, then plug a device into its USB port, and it will charge devices at 2.4 amps.

Charge and drain

When I plugged in my iPhone 5S' white Lightning charging cable to the TransitPlus' USB port, the white LEDs immediately lit up, indicating it was charging. Those lights also show the current capacity of the TransitPlus in 25 percent increments. If my device did not immediately begin charging when I plugged it in, the recessed button near the indicator lights would initiate charging.

After charging up my phone, which was only about 25 percent down, I proceeded to plug in every other device I could find around the office. I spent the afternoon charging tablets, phones, and a Kindle to drain the battery. As expected, the tablets charged more slowly than they would on a wall charger, but the TransitPlus succesfully topped everything up until I had its indicator lights down to nothing.

Plugging the TransitPlus into a wall charges it up in a couple of hours, but I was more interested in finding out how fast you can charge it off a car's 12-volt power point. I plugged it into a Toyota Highlander Hybrid before a 3-hour drive and found that was all it took to get all four charge indicator LEDs to light up.

MyCharge TransitPlus
The TransitPlus just barely fits into this console-mounted 12-volt power point. Josh Miller/CNET

My one caveat about the TransitPlus is that its 12-volt plug only sticks out 1.5 inches from the device. Some cars hide their 12-volt outlets in consoles or dashboard compartments, which might make it impossible to plug the TransitPlus in. To add some flexibility, the TransitPlus' 12-volt plug swings out in three positions: perpendicular with the the long side, perpendicular to the short side, and at an angle.

The wall plug only sticks out from the long side, so the TransitPlus would take up some room on a power strip.

There are quite a few portable battery packs on the market for charging cell phones, most of which offer around 3,000mAh. Many can also be had for quite a bit less than the TransitPlus' $69.99 list price. The integrated wall and 12-volt plugs of the TransitPlus are the primary features that set it apart from the competition, which generally recharge through a USB port.

As its best use, the fact that you can charge a device off the TransitPlus while it is plugged into a wall makes a it an excellent, if bulky, substitute for a simple wall outlet-to-USB adapter. With that use, you will always have a backup power pack with you.